Older JD 300 diesel backhoe and loader starting

I've inherited this tractor from my dad. I have a silly question. Below the key/ignition there is a toggle the clicks into 3 or 4 different positions. Is this some type of choke? Unable to track down what this does - when it is in one of the positions the tractors makes an awful noise when I try and start it. Having troubles starting it this spring and was hoping this lever may be some type of choke. Battery charge on it right now to make sure everything is up and charged.

Not sure of the year - he's had it since mid 70's for sure - and purchased it used. It is a diesel - not sure if some type of glow plug either.